Agree; I use this in my wife's 2007 XK: https://www.amazon.com/gp/product/B06Y42RKPF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I have this one or variants by other companies in all my cars that have CD slots, which are now useless to me. This one I linked to has a particularly strong magnet so it works well with heavier phones or thicker cases (you slide their provided strip of metal between your phone and its case, or you can stick the strip to the back of the phone / case if you wish). No marks on the car, easy to remove, cheap, and works great. And again, this one has a really strong magnet.
I've always been concerned about the air-vent ones; lots of pressure on the plastic. But I take one of those when I travel and rent cars, since most rental cars these days don't have the CD slot.